Centrifugal pumps of this type and in different variants are counted as belonging to the state of the art, and Grundfos pumps of the CR series are referred to in this context. These pumps are operated with a vertically arranged shaft. Thereby, the pump stages are clamped between a foot apart and a head part and are provided with a jacket which surrounds these and which together with the diffusers arranged over one another form an annular channel, via which the fluid which is delivered upwards from the suction port at the lower side of the lowermost impeller through the pump stages, is led back to the delivery connection of the pump. A shaft carrying the impellers passes through the head part of the pump, and there is sealed by way of a mechanical shaft seal integrated in the manner of a cartridge. The shaft end which is led out there at the pump head is connected to the shaft end of an electrical drive motor in a rotationally fixed manner, said drive motor being fastened via a motor stool arranged on the pump head part.
Inherent of the design, considerable forces also act upon the pump shaft in the axial direction, and these must be accommodated by the bearings of the pump or the motor. These forces are essentially created hydraulically. Thus, with the Grundfos pump CR90 for example, axially downwardly directed forces of the magnitude of 900 Newton act at a delivery output of 120 m3 per second, and these forces are to be accommodated by the bearings of the 45 KW motor, by which means a loading of the bearings is given, and this must be taken into account with the design or entails a high wearing of the bearings.